When terminals perform call setup to provide a service in a Wideband Code Division Multiple Access (WCDMA) circuit-based cellular system, the terminals transit into an active state in which they maintain radio resource control (RRC) connection. The terminals in active state can transmit control information or packets through a configured dedicated channel whenever they require the transmission of control information/packet data according to buffer status or wireless channel environment. Therefore, the terminals report measurement information on a serving cell and neighbor cells at a measurement information report period that is set up in advance in order to execute handover. The transmission channel between a terminal and a base station is maintained until the base station and the terminal terminate the service and the terminal releases radio resources used in the service to transit into an idle state. Although the terminal is in the idle state, a network collects measurement information from the terminal at the measurement information report period to perform network management on the basis of a cell to which the terminal belongs. Also, the terminal may report measurement information to the network when the terminal decides that handover triggering is needed.
In a packet-based cellular system, however, a transmission channel for transmitting packet information does not provided dedicatedly to a corresponding terminal until the end of a packet service between the terminal and a base station, even though the terminal is in the active state for the service. In other words, although a logical channel for transmitting packet data continues to exist, radio resources, which are physical channels, are shared by a plurality of terminals under the coverage of a base station. Control operation related to radio resource allocation is carried out by the base station. Specifically, an RRC function and a scheduler of the base station take charge of allocating and scheduling radio resources.
For example, a 3rd-Generation Partnership Project (3GPP) Long Term Evolution (LTE) system is a packet-based system providing services. When RRC connection is set up to provide a packet service between a base station and a terminal in a packet-based cellular system, the terminal transits into the active state. When the service is terminated or no packet data to be transmitted are generated for more than a predetermined time, the terminal may transit into the idle state under the control of the base station.
When the terminal is in the active state, the base station allocates radio resources for transmitting packet data to the terminal according to quality of service (QoS) and burst characteristics. The radio resources are allocated semi-statically, persistently, or dynamically according to scheduling performance in an RRC layer and a medium access control (MAC) layer of the base station.
Generally, the QoS and such burst characteristics of the packet service as packet data size and packet generation frequency are different according to whether the packet service is a real-time service or non-real time service. Also, allocation of radio resources for providing a service is affected as well. This factor is called activity level or activity factor. Ultimately, the scheduler of a base station allocates radio resources for transmitting packet data according to the activity factor.
Meanwhile, when a terminal does not transmit or receive packets in a packet-based cellular system, the terminal needs to execute an operation for saving power. An active-state terminal as well executes a power-saving operation in a packet-based cellular system during a discontinuous reception (DRX) period or a discontinuous transmission (DTX) period to save power consumption. Basically, a terminal executes the power-saving operation according to DRX/DTX period that are set up between the terminal and a base station. To take an example, an active-state terminal remains in a sleep mode for the predetermined DRX/DTX period, and wakes up at the end of the periods to decode control signal blocks transmitted from the base station.
Also, in order to support handover, which is one of the most important functions of a cellular system, the terminal measures quality information not only of a serving cell that is currently on service but also neighbor cells as well and reports the quality information to the base station.
The active-state terminal should execute the power-saving operation in a duration when no data burst out according to the predetermined discontinuous DRX/DTX period in the packet-based cellular system, while transmitting/receiving packet data through radio resources allocated by the scheduler of the base station. Then, the terminal should report the measured quality information of the serving cell and neighbor cells for handover.
FIG. 1 exemplarily shows an operation of an active-state receiving a packet service that is generally performed according to discontinuous DRX/DTX period.
An active-state terminal receiving a service in a packet-based cellular system exchanges packet data with a base station through radio resources addressed by a scheduler of the base station according to scheduling information. The terminal executes a power-saving operation based on DRX/ and/or DTX parameters in a DRX/DTX operation section 12, which is not a packet data exchange section 11, to save power consumed in the terminal. The DRX/DTX parameters basically include DRX/DTX periods 13. The DRX/DTX periods 13 include DRX/DTX duration 14 and monitoring duration 15. In the DRX/DTX duration 14, the terminal does not transmit or receive packets to or from the base station to reduce its power consumption. In the monitoring duration 15, the terminal monitors information transmitted from the base station. The information involves information directing the terminal to receive downlink packets such as paging information.
In order to transmit packet data from the base station to the terminal in the DRX/DTX operation section, the base station transmits to the terminal information directing the terminal to receive data in the monitoring duration. When the terminal receives the data and acknowledges to the base station, the base station transmits downlink packet data.
Also, in order to transmit uplink packet information from the terminal to the base station, the terminal executes one of the following processes after DRX/DTX operation ends. At first, after the terminal ends the DRX/DTX operation, the terminal tries a random access to the base station to receive radio resources allocated thereto. Secondly, the base station transmits scheduling information to the terminal in a duration where the terminal is awake, which is the monitoring duration 15, following the ends of a DRX/DTX period and allocates uplink radio resources. Thirdly, uplink radio resources are allocated in the duration when the terminal is awake according to a protocol predetermined between the base station and the terminal.
Meanwhile, handover is one of the most important functions of a cellular communication system. Active-state terminals should be able to transmit measurement information on a serving cell and neighbor cell periodically or if necessary in order to smoothly perform handover. In the packet data exchange section 11 where packet data are exchanged between the base station and the terminal, the terminal can transmit the measurement information to the base station through one of the following three methods. A first one is that the base station allocates additional uplink radio resources for the report of the measurement information. A second one is that the terminal transmits the measurement information along with packet data by using the allocated uplink radio resources. The third one is that the terminal requests the base station to allocate radio resources to be used for reporting the measurement information through the allocated uplink radio resources.
As described above, since an active-state terminal, too, operates according to DRX/DTX periods to save power in a packet-based cellular system, it is required to develop a method for the terminal performing power-saving operation to report measurement information on a serving cell and neighbor cells for the sake of handover.